Project Summary Musculoskeletal injuries affect 28.6 million Americans of all ages per year, including injuries to tendon, ligament, and muscle. Following injury, tendons heal through scar formation, do not regain pre-injury material properties, and often display aberrant phenotypes that are further exacerbated with aging. The limited capacity of native tendon stem/progenitor cells (TSPCs) to aid in the repair process may contribute to this deficient healing response. Unlike normal tendon, degenerate and aged tendon contains TSPCs that exhibit deficits in clonogenicity, multipotency, and self-renewal capacity, as well as early maturation into senescence. TSPC replacement therapies have the potential to improve tendon healing following injury, but current strategies for delivery of TSPCs are limited in their ability to maintain cell viability and stemness. Such limitations may be overcome by developing biomaterials that maintain TSPC behavior, protect TSPCs immediately post- transplantation, and respond to force-sensitive triggers for on-demand delivery. Delivery of TSPCs using biphasic alginate ferrogels that provide responsive cell release in the presence of a magnetic field may greatly improve tendon healing throughout aging, but this has not yet been explored. Therefore, this study aims to develop and examine a new approach to on-demand TSPC delivery using implantable biphasic ferrogels. We hypothesize that a biomaterial system for delivery of TSPCs (using biphasic alginate ferrogels) will maintain TSPC clonogenicity, multipotency, and self-renewal prior to release, deliver TSPCs on-demand, and ultimately augment tendon following aging and injury. This hypothesis will be tested with the following aims: (1) develop and examine the ability of biphasic ferrogels to maintain TSPC behavior prior to release using cells derived from juvenile, adult, and aged tendons, (2) develop and examine the ability of biphasic ferrogels to deliver TSPCs derived from juvenile, adult, and aged tendons on-demand, and (3) investigate the ability of biphasic ferrogels to augment tendon throughout aging and healing in a clinically-relevant load-bearing rodent Achilles tendon injury model. Success in this effort would have a dramatic impact on individuals suffering from tendon dysfunction following injury and could contribute to the development of on-demand therapeutics for other musculoskeletal diseases. Overall, the project is designed to effectively train the applicant to develop the technical skills needed to establish a successful and independent research program in the future.